The present invention relates to a shaft for golf clubs (hereinafter referred to simply as shaft). More specifically, the present invention provides a grip region of a golf club shaft with improved rigidity.
In golf clubs, lighter shafts are desirable to improve the head speed during the swing. In addition, improved flexural rigidity at the grip is also desired to improve the feel of impact when striking the ball.
Japanese laid-open utility model publication number 63-133261 and Japanese laid-open utility model publication number 4-44968 disclose fiber-reinforced resin shafts where the rigidity of the shaft is adjusted by providing a member made from fiber-reinforced resin disposed over a section of the shaft.
U.S. Pat. No. 3,614,101 discloses a golf club shaft having a sloped section that expands toward the grip end. The sloped section has a gradient of 28/1000, a length of 254 mm, and an outer diameter at the grip end of 20.57 mm. A semi-sloped section having a slope gradient of 10.79/1000 is disposed closer to the end than the sloped section.
Japanese laid-open patent publication number 9-299524 discloses a fiber-reinforced resin golf club shaft having a tapered section toward the grip, a smalldiameter section toward the head, and a tapered center section. The tapered section toward the grip has a gradient between 2/1000 and 10/1000, a length between 200 mm and 600 mm, and a maximum outer diameter between 18 mm and 37 mm.
The golf club shafts disclosed in Japanese utility-model publication number 63-133261 and Japanese laid-open patent publication number 4-44968 are expensive to make. Both publications teach to use separate members which causes the production process to be complex and also substantially increases the cost of production.
Japanese utility model examined publication number 2529041 discloses another fiber reinforced resin shaft. The rigidity of the shaft is adjusted by having a metal layer disposed on the grip section of the shaft. The use of the metal layer also increases the complexity of the production process and substantially increases costs. Furthermore, since fiber-reinforced resin and metal do not have high adhesiveness, the grip section of the shaft is expected to lack durability.
With the shaft disclosed in U.S. Pat. No. 3,614,101, a straight shaft section approximately 150 mm in length is disposed between a sloped shaft section and a semi-sloped shaft section. At each point along the shaft where the sloped section meets the straight section there is a large change in the flexural rigidity of the golf club shaft. Since the straight section abuts two different sloped portions, the shaft has two locations where there is a large change in the flexural rigidity. When a golfer attempts to swing a club designed according to this method, the club shaft has variations in flexure. The flexure depends on a variety of factors including swing speed, cadence, ability and technique of the golfer""s swing. The variations in the flexure of the shaft makes the golf club awkward to use.
Also, in the golf club shaft from Japanese laid-open patent publication number 9-299524 described above, there is a long section toward the end that has a uniform diameter. This section has less flexural rigidity and the kick point is too high. This results in a golf club shaft that is difficult to use.
It is an object of the present invention to provide a golf club shaft which overcomes the drawbacks of the prior art.
It is another object of the present invention to provide an improved grip section in a golf club shaft that overcomes the drawbacks of the prior art.
It is yet another object of the present invention is to provide a golf club shaft and method for producing the same where the rigidity is appropriately high, a kick point is formed at an appropriate position, the shaft is easy to use, and production can be performed inexpensively and easily.
It is an object of the present invention to provide a golf club shaft with a reduced number of parts.
It is another object of the present invention to provide a light weight golf club shaft which has an appropriate hardness and rigidity in the grip section.
It is yet another object of the present invention to provide a light weight golf club shaft with an appropriate hardness and rigidity in the grip section that provides a comfortable feel when hitting a golf ball.
It another object of the present invention to provide a light weight golf club shaft with an appropriate hardness and rigidity in the grip section that minimizes unnecessary wrist movements when hitting a golf ball.
It another object of the present invention to provide a light weight golf club shaft with an appropriate hardness and rigidity in the grip section that provides an appropriate kick point in the shaft.
It another object of the present invention to provide a light weight golf club shaft with an appropriate hardness and rigidity in the grip section that provides a good strength distribution along the shaft.
It is an object of the present invention to form a golf club shaft with a sloped section having a specific slope gradient where production is simplified by reducing the number of required parts. The shaft is light and has appropriate hardness, provides good rigidity at the grip section of the shaft, has good strength distribution along the shaft, and provides an appropriate kick point position along the shaft. The improvements provide a golf club with a good feel when hitting balls. The shaft has a large outer diameter at the grip section which restricts unnecessary movements at the wrists during golf club swinging and thereby improving the aim of the ball.
It is an object of the present invention to provide a golf club shaft having a sloped section with a length of 200-350 mm and a grip end with an outer diameter of 18-25 mm.
It is a further object of the present invention to provide a golf club shaft with a sloped section having a length of 200-350 mm and a grip end with an outer diameter of 18-25 mm which results in improved performance.
It is yet a further object of the present invention to increase the rigidity in the golf club shaft by forming a semi-sloped section at a position further toward the end than the sloped section with a slope gradient of 4/1000-13/1000.
It is yet another object of the present invention to provide a golf club shaft where a golf club head can be easily attached easily to the end of the shaft by forming a uniform-diameter section with a length of 40-125 mm at the end of the shaft.
Briefly stated, the present invention provides for a golf club shaft having an optimal set of materials and sloped sections provides appropriately high rigidity, ease of use, and is inexpensive and easy to manufacture. A sloped section expands toward a grip end of the shaft. The sloped section has a slope gradient from 15/1000 to 35/1000 and a length from 200 to 350 mm. The outer diameter of the grip end is from 18 to 25 mm. On the side of the sloped section toward an end, there is formed a semi-sloped section with a slope gradient from 4/1000 to 13/1000. A kick point is formed at a position from 40% to 46% from the small-diameter end relative to the total shaft length. The number of required parts is small while production is simple. The shaft is light, has appropriate hardness, and. high rigidity at the grip. Furthermore, the strength of the shaft is balanced and provides a good feel when hitting a ball. Production of the golf club shaft can be accomplished with standard materials such as fiber-reinforced resins. By wrapping a fiber-reinforced resin around a mandrel and rolling the material on a base which is heated to an optimal temperature, the strength and rigidity of the shaft can be optimized. Multiple layers can be overlaid to provide any desired strength and rigidity required. The rolled shaft is then heated to set the resin and produce a golf club shaft of optimal performance and reduced cost.
According to an embodiment of the present invention, there is provided for a golf club shaft having a grip end and an other end, comprising: a sloped section expanding toward the grip end, the sloped section having a first slope gradient in a range from 15/1000 to 35/1000, the sloped section having a first length in a range from 200 mm to 350 mm, the grip end having an outer diameter in a range from 18 mm to 25 mm, a semi-sloped section expanding from the other end to the sloped section, the semi-sloped section having a second slope gradient in a range from 4/1000 to 13/1000, the other end having a small diameter, a kick point is located a distance from the small-diameter end, and the distance is in a range from 40 to 46%of a total length of the shaft.
According to another embodiment of the present invention, there is provided for a method for forming a golf club shaft, the steps comprising: wrapping a fiber-reinforced material around a mandrel having a sloped section expanding towards an end of the mandrel to form a wrapped mandrel, applying a first pressure to the wrapped mandrel in a region outside of the sloped section to form a non-pressurized region at the sloped region, applying a second pressure to the non-pressurized region to form a pressurized wrapped mandrel, and heating the pressurized wrapped mandrel to set the fiber reinforced material and form the golf club shaft.
According to yet another embodiment of the present invention, there is provided a method for forming a golf club shaft, the steps comprising: wrapping an inner-layer fiber-reinforced resin material around a mandrel having a sloped section expanding toward an end of the mandrel to form a first wrapped mandrel, the first wrapped mandrel having fibers from the inner-layer fiber-reinforced resin material oriented at an angle in a range from 20 to 70 degrees relative to an axis of the mandrel, heating a rolling base to a first temperature in a range from 30 to 40 degrees C., rolling the first wrapped mandrel on the rolling base at the first temperature to produce a first treated mandrel, the first treated mandrel having the inner-layer fiber-reinforced material adhesed to the mandrel, the step of rolling the first wrapped mandrel includes applying pressure to a section of the mandrel outside the sloped section to form and first non-pressurized region, and applying pressure to the first non-pressurized region, wrapping an outer-layer fiber-reinforced resin material around the first treated mandrel to form a second wrapped mandrel, the second wrapped mandrel having fibers from the outer-layer fiber-reinforced resin material oriented parallel to the axis of the mandrel, heating the rolling base to a second temperature in a range from 20 to 25 degrees C., rolling the second wrapped mandrel on the rolling base at the second temperature to produce a second treated mandrel, the second treated mandrel having the outer-layer fiber-reinforced material adhesed to the inner-layer fiber-reinforced material, the step of rolling the second wrapped mandrel includes applying pressure to a section of the mandrel outside the sloped section to form and first non-pressurized region, and applying pressure to the first non-pressurized region, and heating and setting the second treated mandrel to form the golf club.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.